Disk drives are widely accepted as a cost effective data storage system for a computer, music player, or other data processing devices. As shown in FIG. 1, a disk drive system 10 comprises a magnetic recording medium, in the form of a disk or platter 12 having a hub 13 and a magnetic read/write transducer 14, commonly referred to as a read/write head. The read/write head 14 is attached to or formed integrally with a suspension arm 15 suspended over the disk 12 and affixed to a rotary actuator arm 16. A structural arm 18, supported by a platform 20, is pivotably connected to the actuator arm 16 at a pivot joint 22. A voice coil motor 24 drives the actuator arm 16 to position the head 14 over a selected position on the disk 12.
As a spindle motor (not shown) rotates the disk 12, the moving air generated by the rotating disk in conjunction with the physical features of the suspension arm 15 lifts the read/write head 14 away from the platter 12, allowing the head 14 to glide or fly on a cushion of air slightly above an upper surface of the disk 12. The flying height of the read/write head 14 over the disk surface is typically less than a micron.
An arm electronics module 30 may include circuits that switch the head function between read and write operations, a write driver for supplying write current to the head 14 during write operations and an amplifier for amplifying the read signal. The arm electronics module 30 is connected to the head 14 by flexible conductive leads 32
The configuration and components of the electronics module 30 may vary according to the disk drive design as will be understood by persons familiar with such technology. Although the module 30 may be mounted anywhere in the disk drive 10, a location proximate the head 14 minimizes signal losses and induced noise in the head signals during a read operation. A preferred mounting location for the module 30 comprises a side surface of the structural arm 18 as shown in FIG. 1.
As shown in a partial cross-sectional schematic view in FIG. 2, the disk 12 comprises a substrate 50 and a thin film 52, disposed thereover. The magnetic transducer or head 14 comprises a write head 14A for writing data bits to the disk 12 by altering magnetic domains of ferromagnetic material in the film 52, thereby creating magnetic transitions in the magnetic domains. A read head 14B reads the magnetic transitions to determine the stored data bit.
Data bits and timing information to be written to the disk 12 are supplied by a data processing device 60 (e.g. a computer or music player), in the form of bipolar data pulses in PECL (positive emitter-coupled logic) form. Typically, the PECL bipolar signals representing a logic one and a logic zero differ by about 200 mV or about 450 mV. The incoming data pulses have an absolute voltage of about 2.85V and about 3.3V for a 450 mV differential PECL signal and about 3.1V and about 3.3V for a 200 mV differential PECL signal. The data and timing pulses are supplied to a data write circuit 62 where the data bits are formatted and error detection/correction information appended thereto.
To write data bits, the voice coil motor 18 moves the suspension arm 16 to a desired radial position above the surface of the disk 12 while the spindle motor rotates the disk 12 to move a circumferential region to be written under the write head 14A. A write driver 66A of a preamplifier 66 (in one embodiment disposed within the electronics module 30) supplies a programmed write current (in certain applications between about 10 mA and 70 mA) to the write head 14A responsive to the signal from the data write circuit 62. The write driver 66A scales up the relatively low voltage levels representing the data bits to a voltage range between about +/−6V and +/−10V. In one embodiment the write driver 66A converts the PECL signals to logic signals having a larger differential voltage, such as about 3.3V. Typical absolute voltages are −1.7V to −5.0V with a 3.3V differential or 1.7V to 5.0V with a 3.3V differential. The voltage conversion is desired to properly drive metal-oxide semiconductor field effect transistors (MOSFETS) (not shown) that supply write current to the write head 14B. The write driver 66A also shapes the write current signal waveform to optimize the data writing process.
Write current supplied by the write driver 66A to the write head 14A (magnetically coupled to a magnetically permeable core not shown) creates a magnetic field that extends from the core across an air gap between the write head 14A and the disk 12. The magnetic field alters a region of ferromagnetic domains in the thin film 52 to store the data bits as magnetic transitions.
The direction of the magnetic field generated by the write head 14A, and thus the direction of the altered ferromagnetic domains, is responsive to the direction of current flow through the write head 14A. Current supplied in a first direction through the write head 14A causes the domains to align in a first direction (representing a date 0 for example) and current supplied in a second direction (representing a data 1 for example) causes the domains to align in a second direction.
In the read mode transitions between adjacent domains are detected to determine the stored data bit. The read head 14B (comprising either a magneto-resistive (MR) sensor or an inductive sensor) senses the magnetic transitions in the thin film 52 to detect the stored data bits. The MR sensor produces a higher magnitude output signal in response to the magnetic transitions, and thus the output signal exhibits a greater signal-to-noise ratio than an output signal produced by the inductive sensor. The MR sensor is thus preferred, especially when a higher a real data storage density is desired. State-of-the-art MR read heads include giant magnetoresistive (GMR) heads and tunneling magnetoresistive (TMR) heads.
The suspension arm 16 moves the head 14 while the disk 12 rotates to position the read head 14B above a magnetized region to be read. A DC (direct current) bias voltage of between about 0.025V and about 0.3V is supplied to the read head 14B by a read circuit 66B of the preamplifier 66. Magnetic domains in the thin film 52 passing under the read head 14B alter a resistance of the magneto-resistive material, imposing an AC (alternating current) component on the DC bias voltage. The AC component representing the read data bits has a relatively small magnitude (e.g., several millivolts) with respect to the DC bias voltage.
The differential read circuit output signal, having an amplitude in a range of several millivolts, is input to a signal processing stage 102 followed by an output or converter stage 104. Typically, both the signal processing stage 102 and the output stage 104 are elements of the preamplifier 66. The signal processing stage 102 amplifies the signal to increase the signal's signal-to-noise ratio. The output stage 104 scales up the head signal voltage to a peak voltage value in a range of several hundred millivolts, supplying the scaled-up signal to channel circuits of a channel chip 106 through an interconnect 108. The channel chip 106 detects the read data bits from the voltage pulses, while applying error detection and correction processes to the read data bits. The read data bits are returned to the processing device 60 via a user interface 110 (e.g., SATA, SCSI, SAS, PCMCIA interfaces).
In other data storage systems the head 14 operates with different types of storage media (not shown in the Figures) comprising, for example, a rigid magnetic disk, a flexible magnetic disk, magnetic tape and a magneto-optical disk.
To increase storage capacity, a disk drive may comprise a plurality of stacked parallel disks 12. A read/write head is associated with each disk to write data to and read data from a top and bottom surface of each disk.